Zinc oxide (ZnO) is a direct transition semiconductor having a bandgap energy of about 3.4 eV and having a quite high exciton binding energy of 60 meV, and thus can realize a light-emitting device with a high efficiency and low power consumption. In addition, zinc oxide has characteristics such as a low raw material price and harmless to environment and human body and thus can provide a light-emitting device which is low in price and excellent in environmental properties.
However, ZnO is susceptible to have a defect of an oxygen vacancy and interstitial Zn atom, and has been regarded as difficult to form a p-type conductive layer, but many studies are under way to make ZnO p-type using nitrogen (N) as an acceptor impurity and fabricate a light emitting-device with a high efficiency using ZnO semiconductor.
The semiconductor light-emitting device using a ZnO single crystal substrate is disclosed, for example, in following Patent Documents 1, 2, and 3, and a method of manufacturing ZnO crystal into which nitrogen (N) is introduced, though on a sapphire substrate, and a method of manufacturing a ZnO LED are disclosed in Patent Document 4.
Patent Document 1: JP 2004-247411A
Patent Document 2: JP 2004-247681A
Patent Document 3: JP 2004-296821A
Patent Document 4: JP 2004-221352A